diff --git a/metropolis/pkg/efivarfs/efivarfs.go b/metropolis/pkg/efivarfs/efivarfs.go
index e731069..8132579 100644
--- a/metropolis/pkg/efivarfs/efivarfs.go
+++ b/metropolis/pkg/efivarfs/efivarfs.go
@@ -24,8 +24,8 @@
 	"fmt"
 	"os"
 	"path/filepath"
-	"strings"
 
+	"github.com/google/uuid"
 	"golang.org/x/text/encoding/unicode"
 )
 
@@ -58,20 +58,23 @@
 }
 
 // ReadLoaderDevicePartUUID reads the ESP UUID from an EFI variable. It
-// depends on efivarfs being already mounted. It returns a correct lowercase
-// UUID, or an error.
-func ReadLoaderDevicePartUUID() (string, error) {
+// depends on efivarfs being already mounted.
+func ReadLoaderDevicePartUUID() (uuid.UUID, error) {
 	// Read the EFI variable file containing the ESP UUID.
 	espUuidPath := filepath.Join(Path, "LoaderDevicePartUUID-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f")
 	efiVar, err := os.ReadFile(espUuidPath)
 	if err != nil {
-		return "", fmt.Errorf("couldn't read the LoaderDevicePartUUID file at %q: %w", espUuidPath, err)
+		return uuid.Nil, fmt.Errorf("couldn't read the LoaderDevicePartUUID file at %q: %w", espUuidPath, err)
 	}
 	contents, err := ExtractString(efiVar)
 	if err != nil {
-		return "", fmt.Errorf("couldn't decode an EFI variable: %w", err)
+		return uuid.Nil, fmt.Errorf("couldn't decode an EFI variable: %w", err)
 	}
-	return strings.ToLower(contents), nil
+	out, err := uuid.Parse(contents)
+	if err != nil {
+		return uuid.Nil, fmt.Errorf("value in LoaderDevicePartUUID could not be parsed as UUID: %w", err)
+	}
+	return out, nil
 }
 
 // CreateBootEntry creates an EFI boot entry variable and returns its
diff --git a/metropolis/pkg/sysfs/BUILD.bazel b/metropolis/pkg/sysfs/BUILD.bazel
index 068f9f6..06995e2 100644
--- a/metropolis/pkg/sysfs/BUILD.bazel
+++ b/metropolis/pkg/sysfs/BUILD.bazel
@@ -8,4 +8,5 @@
     ],
     importpath = "source.monogon.dev/metropolis/pkg/sysfs",
     visibility = ["//metropolis:__subpackages__"],
+    deps = ["@com_github_google_uuid//:uuid"],
 )
diff --git a/metropolis/pkg/sysfs/block.go b/metropolis/pkg/sysfs/block.go
index 9f9ebf8..c7cbbd7 100644
--- a/metropolis/pkg/sysfs/block.go
+++ b/metropolis/pkg/sysfs/block.go
@@ -26,6 +26,8 @@
 	"path/filepath"
 	"strconv"
 	"strings"
+
+	"github.com/google/uuid"
 )
 
 // PartUUIDMap returns a mapping between partition UUIDs and block device
@@ -60,12 +62,12 @@
 
 // DeviceByPartUUID returns a block device name, given its corresponding
 // partition UUID.
-func DeviceByPartUUID(uuid string) (string, error) {
+func DeviceByPartUUID(id uuid.UUID) (string, error) {
 	pm, err := PartUUIDMap()
 	if err != nil {
 		return "", err
 	}
-	if bdev, ok := pm[strings.ToLower(uuid)]; ok {
+	if bdev, ok := pm[id.String()]; ok {
 		return bdev, nil
 	}
 	return "", ErrDevNotFound